1. Field of the invention
This invention relates to a method of regulating an inductance (or obtaining a selected inductance) of a three-layer structural spiral inductor having a structure wherein a spiral conductive part is disposed between two ground electrodes through an insulating material.
2. Prior Art
In FIG. 2 and FIG. 3, a three-layer structural spiral inductor 1 to which this invention can be applied is shown. FIG. 2 is a bottom plan view, and FIG. 3 is a sectional view and is taken along the line III--III of FIG. 2.
The three-layer structural spiral inductor 1 has a substrate 2 comprising an electric insulating material, for example, a resin such as a glass-epoxy resin or ceramics. A plurality of wiring patterns 3, 4 and 5 are formed on one main surface of the substrate 2, and a first ground electrode 6 is formed on the other main surface of the substrate 2. A second ground electrode 7 is formed inside the substrate 2 so as to oppose the first ground electrode 6. Further, a spiral inductor conductive part 8 is formed inside the substrate 2 between the first ground electrode 6 and the second ground electrode 7.
A first through hole joint (or first through hole conductor) 10 is provided in the substrate 2 so as to electrically connect the outer peripheral end 9 of the inductor conductive part 8 and the first and second ground electrodes 6 and 7. On the other hand, a second through ho 1 e j o int ( or second through hole conductor) 12 is provided in the substrate 2 so as to electrically connect the inner peripheral end 11 of the inductor conductive part 8 and the specific wiring pattern 3. Gaps 13 and 14 are provided between the second through hole joint 12 and each of the first and second ground electrodes 6 and 7, respectively, so that the second through hole joint 12 is not electrically connected to either the first or the second ground electrode 6, 7.
The three-layer structural spiral inductor 1 as mentioned above is used for a voltage-controlled oscillator, for example, and parts which construct an oscillation circuit are packaged on the substrate 2.
Conventionally, the three-layer structural spiral inductor 1 mentioned above was (1) used without any regulation, and (2) in case this conductor 1 was used for a resonance system, a variable element such as a trimmer capacitor was connected to the outside and the resonance system was regulated thereby.
However, in the case of (1), since the inductor 1 was used without any regulation, there was a problem, that is, the inductance given by the inductor conductive part 8 and a dispersion of the surrounding parts could not be rectified.
On the other hand, in the case of (2), since other parts such as a variable element were required, the cost would rise and the area of the substrate 2 became enlarged because of the package of the above variable element.